“I think this is just another big, bloated bureaucracy,” she said. “I think it’s just there to raise revenue for the city. This is not going to benefit anyone but them.”

Approved last year by the Boston City Council in a sweeping effort to crack down on irresponsible landlords and bring problem properties up to code, the ordinance has received a cool reception from property owners, who have shown their displeasure with its cost and intrusion by not registering, at least not yet.

Some 40,000 units have been added to the registry, less than 30 percent of the estimated total. Given the slow response, city officials extended the original Aug. 1 deadline by a month and say the pace of registration has picked up as more landlords learn about the requirement.

For the first time, the regulation requires that all private rental units be registered every year. Starting in January, apartments must be inspected every five years, except for owner-occupied buildings with six or fewer units.

City officials say that required inspections will take aim at a longstanding problem: poorly maintained apartments that fail to meet basic sanitary and safety codes. Focusing on landlords who have been cited in the past, inspectors will examine homes for overcrowding, fire hazards, mold, and infestations, among other violations.

Currently, nearly all inspections are prompted by complaints. Inspections are supposed to take place whenever new tenants move in, but almost no landlords inform the city.

“With complaint-driven inspections, we’re only getting at the tip of the iceberg,” said Brian Swett, who oversees the Inspectional Services Department as the city’s chief of environment and energy.“We have a right and a responsibility to make sure tenants have safe and healthy housing.”

Supporters say the inspections will uncover dangerously overcrowded apartments, such as the one in Allston where a Boston University student died in a fire this spring. Nine other residents and six firefighters were injured.

The landlord allegedly allowed 19 people to live in a two-family home.

“That house hadn’t had a proactive inspection in 20 years,” Swett said.

In 2009, a father and his two sons died in an illegal Quincy apartment when a fire broke out, blocking the lone exit.

“It’s been a challenge for fire chiefs across the state to ferret out these illegal apartments,” said Jennifer Mieth, spokeswoman for the state fire marshal’s office.

But property owners say the requirements are too costly and intrusive, and they have been calling city councilors in hope of changing the law. Technical difficulties in registering online have caused further aggravation.

“My office has been bombarded with complaints,” said Charles Yancey, a city councilor and mayoral hopeful who has called for a public hearing on the ordinance. “I think the responsible thing to do is to take a second look.”

Yancey, who backed the ordinance and believes it is well intentioned, says landlords have raised a number of concerns, particularly about the annual registration costs. Many say that they should have to register less frequently and that the city should focus its inspections on properties that have drawn complaints.

“It was never intended to be a revenue-generator,” he said. “I’m not convinced in hindsight it’s necessarily the right approach.”

City officials say they are redoubling efforts to notify landlords about the requirement, posting billboards around the city, mailing postcards to owners and management companies, and including brochures with water-sewer bills.

Two-third of the city’s housing is rental, 2010 Census figures show. In neighborhoods like Mission Hill, Allston, Chinatown, and Fenway, the percentage is well over 80 percent.

Greg Vasil, chief executive of the Greater Boston Real Estate Board, said many landlords are blanching at the cost and are likely to pass along the expense to their tenants. The law caps registration fees at $2,500 per building, $5,000 per complex.

He had also heard from landlords who believe the city is casting too wide a net by setting out to inspect all properties. “Trying to do everything at once is impossible,” he said.

Jason Gell, a Boston broker and owner, said that by making registrations universal, the city’s reach exceeded its grasp.

“What the city was trying to do was good,” he said. “But what they ended up doing is ridiculous. It turned what was pretty well intentioned at heart into a profit center.”

Swett dismissed that notion, saying fees will be put toward enforcing the ordinance. In time, the city will publish a list of persistent offenders to alert potential tenants.

Swett said that the city modeled the inspection program on similar efforts in Baltimore, Minneapolis, and Cleveland, but that Boston’s requirements are more comprehensive. He said that the deadline for registration would not be extended again and that landlords who fail to meet it could be fined $300 a month per unit.

Yet officials said they will be lenient with landlords who intend to register, since the program is new. “We knew this was not going to be easy,” Swett said. “It’s a challenge because we’re starting at zero.”

Seeking to allay concerns, the city’s Inspectional Services Department held an informational session this month, drawing some 3o property owners and managers.

Toney Jones, assistant director of the department’s housing division, handed out folders and fliers, circled the room answering questions, and acknowledged the many pitfalls that have complicated online registration.

“Is it a foolproof system? I say no. Nothing is completely foolproof,” Jones said. “It’s new, and we’re all trying to get through this. I sincerely appreciate your patience.”

Heavy traffic to the website has caused a number of problems, he said.

Landlords who have a bad history with the city will be targeted first for inspections, he said. The goal is to inspect about 30,000 units a year, and the city plans to hire additional inspectors.

“If you’ve never had a problem with [inspectional services] before, your chances of getting on the inspection list at first are slim to none,” he said, adding that
the city hopes to inspect every rental unit in Boston within five years.